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Does the galaxy NGC1052-DF2 falsify Milgromian dynamics?
ARISING FROM P. van Dokkum et al. Nature 555, 629-632 (2018); https://doi.org/10.1038/nature25767
An international group of astronomers has debunked another premature claim that a leading modified gravity theory is dead.
The earlier claim in the prestigious journal Nature neglected a subtle environmental effect in the theory known as Modified Newtonian Dynamics (MOND).
The claim came from the slowness of the motions within a distant dwarf galaxy. The authors argue that its extra gravity in MOND would speed up these motions. However, they did not consider that the gravitational environment of the dwarf could affect motions within it. If it is close to a massive galaxy - which is the case here - then the motions within the dwarf would be slower.
"This effect has been known for a long time," said Hosein Haghi, a professor in the physics department at Zanjan, Iran. "These Nature authors were unaware of our papers on how to include it. Our calculations of the effect were confirmed by another group."
Galaxies rotate so quickly that they should fly apart. This can be avoided in two ways. One is to invoke a halo of dark matter around every galaxy. However, dark matter particles have never been discovered. The other way is to modify the law of gravity on astronomical scales. This MOND approach nicely explains the regularities in galactic rotation curves.
"There have been many premature claims on the death of MOND in very influential journals," said lead author Pavel Kroupa, a professor at the University of Bonn in Germany. "So far, none stand up to detailed scrutiny."
"Our more conventional statistical analysis of the data shows that MOND works fine here", says Indranil Banik, a recent PhD graduate from the University of St Andrews. "In this case, we are not the only group pointing out problems with the earlier Nature paper."
Reference link: https://www.nature.com/articles/s41586-018-0429-z